1. Field of the Invention
The present invention relates to an axle driving system in which a hydrostatic transmission (hereinafter referred to as an xe2x80x9cHSTxe2x80x9d), axles and a power transmitting mechanism are integrally provided in a housing, and more particularly to an axle driving system in which the width of the portion of the housing which houses the HST and power transmitting mechanism is smaller than in conventional systems.
2. Related Art
A conventional axle driving system houses the HST, axles and a driving gear train for interlocking the HST with the axles in a common housing. The HST is constructed so that a hydraulic pump is disposed on a horizontal portion of a center section which is L-like-shaped and a hydraulic motor is disposed on the vertical portion of the same. The hydraulic motor is positioned to one side of the axle. The hydraulic pump and hydraulic motor are fluidly connected to each other by a closed fluid circuit formed in the center section. The hydraulic pump is driven by a prime mover provided on the vehicle so as to drive the hydraulic motor and then the axles through a driving gear train. Such a construction is disclosed, for example, in U.S. Pat. Nos. 5,163,293 and 5,335,496.
The hydraulic pump and hydraulic motor in the conventional technique, are disposed side-by-side and to one side of the axles. As such, the width of the HST is larger which results in the lateral width of the common housing for both the pump and motor also being larger. Furthermore, an output shaft of the hydraulic motor extends to one side of the vehicle to transmit power therefrom to a differential gear unit through gears of a driving gear train, so as to drive the axles. An unused space is formed at a side of the gear train and between the HST pump and the axles.
Further, when the HST and the driving gear train for driving the axles by the output shaft of the HST are housed in a common housing, a foreign object, such as iron powder produced by the driving gear train, may enter into the HST. This can adversely affect operation of the HST or various parts thereof.
The axle driving system of the present invention is constructed so that the HST center section is formed in such a manner that the extended phantom plane of the motor mounting surface of the center section passes in the vicinity of the axis of the pump shaft of the hydraulic pump. The pump shaft extends substantially perpendicular to the axles. The motor shaft of the hydraulic motor extends substantially in parallel thereto. The hydraulic pump is disposed between the hydraulic motor and the axles. Hence, the width of the housing is made smaller so as to be compact in size. The axle driving system, which is smaller in lateral width, is provided with a wide swinging space for the running wheels of the vehicle and is extremely effective for a vehicle having freely steerable wheels mounted thereon.
Further, the present invention divides the housing into two separate chambers for housing the HST and for housing a driving gear train and axles. A partition for dividing the two chambers is provided with an oil filter so that both chambers can be filled with common oil. This improves the durability of the HST and reduces the manufacturing cost.